B5.9G, B5.9LPG, B Gas Plus, B LPG Plus – Fuel Consumption Excessive

Symptom Tree  

Electronic fault codes are active

For instructions on how to read active fault codes, refer to Procedure 101-007 (Electronic Controlled Fuel System) in Section 1. If fault codes are active, contact a Cummins Authorized Repair Facility.


Fuel consumption and/or oil consumption data are inaccurate

Verify fuel consumption and/or oil consumption data. Refer to the engine data specifications.


Vehicle is not being fueled completely

Verify all fuel tank supply valves are open and the tanks contain fuel.


Vehicle has changed routes or loads

Consider operating environment and its effect on fuel economy. Adverse weather, strong head winds, variable routes, and heavier loads can increase fuel consumption.


Operator technique is not correct

Explain correct engine operation to the operator. Refer to Procedure 101-999 (Operating Instructions — Overview) in Section 1.


Fuel consumption is changing due to seasonal or operational changes

Review fuel consumption records for the past 3 to 6 months to determine the effects of seasonal or operational changes.


Fuel grade is not correct for the application or the fuel quality is poor

Operate the engine from a tank of high-quality fuel. Refer to Procedure 018-002 (Fuel Recommendations and Specifications) in Section V.


Fuel leak

Check the fuel lines, fuel connections, and fuel filters for leaks using the combustible gas detector service tool. Refer to a Cummins Authorized Repair Facility.


Drivetrain is not correctly matched to the engine

Check for correct gearing and drivetrain components. Refer to the OEM vehicle specifications.


Coolant temperature is below specification

Refer to the Coolant Temperature is Below Normal symptom tree.


Lubricating oil level is above specification

Check the oil level. Verify the dipstick calibration and oil pan capacity. Fill the system to the specified level. Refer to the OEM service manual.


Wheel alignment is not correct (tractor or trailer)

Check the wheel alignment. Refer to the OEM service manual and the manufacturer’s instructions.


Hubometer or odometer is miscalibrated

Check the hubometer and odometer calibrations. Calibrate or replace the hubometer or odometer, if necessary. Calculate fuel consumption with new mileage figures.


Speedometer is malfunctioning or the road speed is excessive

Calibrate the speedometer. Refer to the OEM service manual.


Ignition coil malfunctioning

Check the ignition coil. Refer to Procedure 013-012 (Ignition Coils) in Section 6 .


Spark plug(s) damaged or incorrect gap

Inspect plug(s). Refer to Procedure 013-016 (Spark Plugs (Standard)) in Section 6.


Battery voltage is low or bad ground connection at battery

Check the batteries. Check the battery circuit. The battery cable ground must measure within OEM specifications for voltage drop under electrical load. Refer to the OEM service manual.


Exhaust system restriction is above specification

Check the exhaust system for restrictions. Refer to the OEM service manual.


Air intake or exhaust leaks

Check for loose or damaged piping connections and missing pipe plugs. Check the turbocharger and exhaust manifold mounting. Refer to Procedure 010-058 (Air Intake Piping) in Section 3 or a Cummins Authorized Repair Facility.


Charge air cooler is restricted or leaking

Inspect the charge air cooler for air restrictions or leaks. Refer to Procedure 010-027 (Charge-Air Cooler) in Section 5.


Air filter is restricted

Check the air filter for restrictions. Refer to Procedure 010-059 (Air Cleaner Restriction) in Section 4.


Overhead adjustments are not correct

Measure and adjust the overhead settings. Refer to Procedure 003-004 (Overhead Set) in Section 6.

Contact a Cummins Authorized Repair Facility

Last Modified:  16-Feb-2005